This invention relates generally to apparatus for use in material cutting operations and, more particularly, to apparatus for use with center-opening saw blades having an inner sawing edge for improving the accuracy and quality of the saw cut.
Center-opening saw blades are used in the cutting of hard, brittle materials of the type used in the manufacture of electrical components, such, for example, as silicon, germanium, quartz, sapphire, garnet and the like. Such center-opening saw blades are formed of thin, high-strength sheet metal and have an inner circular edge provided with a fine coating of natural diamond embedded in a galvanized bonding material. The outer diameter of the saw blade is obtained using an appropriate ring. In manufacture, the saw blade is stretched on a drum kiln to provide a high modulus for the saw blade which resists lateral forces.
The width or span of the saw blade is of great importance to the accuracy and quality of the cut obtained by the saw blade. The out-of-roundness error of the center opening about which the cutting edge is provided must be maintained at a minimum. It is also important to keep the sizes of the clamping collars and spanning edge rings which are used in the spanning or tensioning of the saw blade to a minimum. This is difficult to achieve, however, in saw blades having large diameters, such as about 21 inches or larger.
Apparatus for spanning or applying tension to centeropening saw blades having inner cutting edges are known. In this connection, reference is made to U.S. Pat. No. 3,955,551 and to German patent application No. DE 28 41 653. In particular, apparatus is disclosed in No. DE 28 41 653 wherein the spanning or tensioning of the blade is not produced through the use of a spanning edge. Rather, the saw blade is stretched by the provision, between a ring groove within the clamping collar and a correspondingly profiled spanning ring, of means whose position is axially adjustable through a large number of set screws for engaging a region of the saw blade close to its outer edge at the ring groove. When it is desired to apply a greater tension to the saw blade, such as where larger diameter saw blades are used, it is necessary that the blades project deeply into the ring groove to provide sufficient strength.
A highly accurate and true circular track for the inner cutter edge of the saw blade is achieved by spanning the saw blade. Deviations in the roundness of the center opening in the saw blade are obtained in the case where the radius of the center-opening is too small by stretching the saw blade outwardly and through a partial axial bending of the saw blade by means of the spanning ring provided at the groove of the restraining collar. Depending upon the degree of true roundness of the saw blade opening and the heterogeneity of the saw blade material, the spanning ring will deform axially to a greater or lesser extent and will also obtain a slanted or oblique position with respect to the axis of rotation of the saw blade, thereby affecting the alignment of the machine to the detriment of the quality of the cut obtained. Such conventional techniques are also disadvantageous in that it is not possible to disassemble the saw blade to rotate the same outside of the machine in order to reduce set-up time.